A conventional method of providing piles is to drive a one piece hollow steel casing into the ground to a sufficient depth and thereafter to pour concrete into the interior of the casing (with or without reinforcement) to provide a steel cased concrete pile.
Various methods have been employed in driving such piles including top drive with a hammering action either by the user or a larger mass or a relatively small mass vibrating at a high frequency, or bottom drive using similar techniques, or jacking by applying a downward force to the pile top from an hydraulic jack interposed between the pile top and a fixed reactive member, for example an existing building structure.
As a result of the cost of material employed, piles of the type described above are relatively expensive and attempts have been made in the past to utilize hollow concrete piles which are less expensive to manufacture.
One proposal has involved the use of sectional hollow concrete piles which are driven from above utilizing a pile section carrier or mandrel. Clearly, concrete piles cannot tolerate the same compressive impact loads as steel piles and so that they can be economically driven on past concrete pile driving operations, have involved threading the pile sections onto a central steel mandrel which carried at its forward end a sacrificial nose, the outside diameter of which is slightly greater than the outside diameter of the cylindrical concrete sections. With this arrangement the driving force from the pile driving hammer is transmitted to the nose by the central steel mandrel and the pile sections are simply carried down with the mandrel. When a sufficient depth of pile has been driven, the mandrel can be removed leaving the concrete sections and sacrificial nose in the ground. If desired, the hollow concrete pile can then be filled with reinforcement and concrete.
The method described above is disadvantageous in that if a pile of relatively long length is required, it is often necessary to interrupt the pile driving sequence and insert a longer mandrel after having threaded it through additional pile sections.
It is an object of the present invention to obviate or mitigate these disadvantages.